For further help with Coding Bat (Java), please check out my books. I am also available for tutoring.
Here are my solutions to the Map-2 section on CodingBat.
word0:
public Map<String, Integer> word0(String[] strings) {
Map<String, Integer> map = new HashMap<String, Integer>();
for (int i = 0; i < strings.length; i++) {
map.put(strings[i], 0);
}
return map;
}
wordLen:
public Map<String, Integer> wordLen(String[] strings) {
Map<String, Integer> map = new HashMap<String, Integer>();
for (int i = 0; i < strings.length; i++) {
String tmp = strings[i];
map.put(tmp, tmp.length());
}
return map;
}
pairs:
public Map<String, String> pairs(String[] strings) {
Map<String, String> map = new HashMap<String, String>();
for (int i = 0; i < strings.length; i++) {
String tmp = strings[i];
String first = String.valueOf(tmp.charAt(0));
String last = String.valueOf(tmp.charAt(tmp.length() - 1));
map.put(first, last);
}
return map;
}
wordCount:
public Map<String, Integer> wordCount(String[] strings) {
Map<String, Integer> map = new HashMap<String, Integer>();
for (int i = 0; i < strings.length; i++) {
String tmp = strings[i];
if (map.containsKey(tmp)) {
int count = map.get(tmp);
map.put(tmp, count + 1);
} else {
map.put(tmp, 1);
}
}
return map;
}
firstChar:
public Map<String, String> firstChar(String[] strings) {
Map<String, String> map = new HashMap<String, String>();
for (int i = 0; i < strings.length; i++) {
String key = String.valueOf(strings[i].charAt(0));
if (map.containsKey(key)) {
String val = map.get(key) + strings[i];
map.put(key, val);
} else {
map.put(key, strings[i]);
}
}
return map;
}
wordAppend:
public String wordAppend(String[] strings) {
Map<String, Integer> map = new HashMap<String, Integer>();
String result = "";
for (int i = 0; i < strings.length; i++) {
String key = strings[i];
if (map.containsKey(key)) {
int val = map.get(key);
val++;
if (val % 2 == 0) {
result += key;
}
map.put(key, val);
} else {
map.put(key, 1);
}
}
return result;
}
wordMultiple:
public Map<String, Boolean> wordMultiple(String[] strings) {
Map<String, Integer> counts = new HashMap<String, Integer>();
Map<String, Boolean> result = new HashMap<String, Boolean>();
for (int i = 0; i < strings.length; i++) {
String key = strings[i];
if (counts.containsKey(key)) {
int val = counts.get(key);
val++;
counts.put(key, val);
} else {
counts.put(key, 1);
}
result.put(key, counts.get(key) >= 2);
}
return result;
}
allSwap:
public String[] allSwap(String[] strings) {
Map<String, Integer> map = new HashMap<String, Integer>();
for (int i = 0; i < strings.length; i++) {
String key = String.valueOf(strings[i].charAt(0));
if (map.containsKey(key)) {
// swap
int pos = map.get(key);
String tmp = strings[pos];
strings[pos] = strings[i];
strings[i] = tmp ;
// delete
map.remove(key);
} else {
map.put(key, i);
}
}
return strings;
}
firstSwap:
public String[] firstSwap(String[] strings) {
Map<String, Integer> map = new HashMap<String, Integer>();
for (int i = 0; i < strings.length; i++) {
String key = String.valueOf(strings[i].charAt(0));
if (map.containsKey(key)) {
int val = map.get(key);
if (val == -1) {
continue;
}
// swap
int pos = map.get(key);
String tmp = strings[pos];
strings[pos] = strings[i];
strings[i] = tmp ;
// set a flag
map.put(key, -1);
} else {
map.put(key, i);
}
}
return strings;
}
For further help with Coding Bat (Java), please check out my books. I am also available for tutoring.
Just another solution to wordMultiple.
Instead of making two HashMaps; just use one.
public Map wordMultiple(String[] strings) {
Map map = new HashMap();
for (String s : strings){
if (map.containsKey(s) == false){
map.put(s, false);
} else {
map.put(s, true);
}
}
return map;
}
public Map wordMultiple(String[] strings) {
Map map = new HashMap();
for (String s : strings){
if (map.containsKey(s) == false){
map.put(s, false);
} else {
map.put(s, true);
}
}
return map;
}
What’s with the angled brackets getting deleted during copy and paste?
Just look up how to properly insert source code in WordPress comments. You probably need a special tag for that.
public String[] firstSwap(String[] strings) {
Map map = new HashMap();
Map store = new HashMap();
Map counter = new HashMap();
for(int i = 0; i 2){
break;
}
if(map.containsKey(key)){
String temp = strings[store.get(key + map.get(key))];
strings[store.get(key + map.get(key))] = strings[i];
strings[i] = temp;
map.remove(key);
store.put(strings[i], i);
}else{
store.put(strings[i], i);
map.put(key, strings[i].substring(1));
}
}
return strings;
}
Question: How do I stop coming up with redundant solutions like this on the first attempt to the question? This been happening a lot.
public String[] firstSwap(String[] strings) {
Map map = new HashMap();
Map store = new HashMap();
Map counter = new HashMap();
for(int i = 0; i 2){
break;
}
if(map.containsKey(key)){
String temp = strings[store.get(key + map.get(key))];
strings[store.get(key + map.get(key))] = strings[i];
strings[i] = temp;
map.remove(key);
store.put(strings[i], i);
}else{
store.put(strings[i], i);
map.put(key, strings[i].substring(1));
}
}
return strings;
}
Never mind, the question was too general and the whole solution will not post.
Great site, Gregor!
I came up with a slightly more concise wordCount solution:
public Map wordCount(String[] strings) {
Map map = new HashMap();
for(String s:strings)
map.put(s, Collections.frequency(Arrays.asList(strings), s));
return map;
}
After a lot of frustration and re-thinking, it turns out wordAppend doesn’t even need a map. Just one forward loop with a recurring back-looking loop:
public String wordAppend(String[] strings) {
String output= “”;
int count = 0;
for (int i = 0; i-1; j–){
if (strings[j] == strings[i]) count++;
}
if (count % 2 == 0) output += strings[i];
count = 0;
}
return output;
}
The code got snipped. Forgot to use tags. Here it is properly:
public String wordAppend(String[] strings) {
String output= "";
int count = 0;
for (int i = 0; i-1; j--){
if (strings[j] == strings[i]) count++;
}
if (count % 2 == 0) output += strings[i];
count = 0;
}
return output;
}
Not sure if I mis-pasted the code or it was snipped again?
public String wordAppend(String[] strings) {
String output= "";
int count = 0;
for (int i = 0; i-1; j--){
if (strings[j] == strings[i]) count++;
}
if (count % 2 == 0) output += strings[i];
count = 0;
}
return output;
}
Another solution to firstSwap using Map and ArrayList.
public String[] firstSwap(String[] strings) {
Map proMap = new HashMap();
List proList = new ArrayList();
for(int i=0; i<strings.length; i++){
String key = String.valueOf(strings[i].charAt(0));
if(proMap.containsKey(key) && !(proList.contains(key))){
int pos = proMap.get(key);
String tmp = strings[pos];
strings[pos] = strings[i];
strings[i] = tmp;
proList.add(key);
} else{
proMap.put(key, i);
}
}
return strings;
}
wordLen:
public Map wordLen(String[] strings) {
return Arrays.stream(strings)
.collect(Collectors.toMap(s -> {
return s;
}, String::length, (a, b) -> b));
}
Try doing it without those inbuilt functions! You’re cheating yourself out of learning basic programming skills. Regardless of what you may think, you will not be able to skip that step.
pairs:
public Map pairs(String[] strings) {
return Arrays.stream(strings)
.collect(Collectors
.toMap(s -> {
return String.valueOf(s.charAt(0));
}, s -> String.valueOf(s.charAt(s.length() – 1)), (a, b) -> b));
}
wordAppend:
public String wordAppend(String[] strings) {
Map map = new HashMap();
String result = “”;
for (String key : strings) {
if (map.containsKey(key)) {
int val = map.get(key);
val++;
if (val % 2 == 0) {
result += key;
}
map.put(key, val);
} else {
map.put(key, 1);
}
}
return result;
}